The invention of the present patent application relates to a vehicle headlamp in which a lighting device unit for providing a forward beam illumination in a predetermined light distribution pattern is accommodated within a lamp body.
There is known a headlamp of the type in which the lighting device unit is accommodated in the lamp body. Japanese Patent Publication Hei-1-197901 discloses a technique, though it is that of a fog lamp, in which a movable reflecting mirror of the lighting device unit is horizontally swung in accordance with a steering angle to thereby horizontally displace a light distribution pattern. If the technique is applied to the vehicle headlamp, it is possible to enhance a visibility of the road surface in front of a vehicle when the vehicle turns to the right or left.
The technique of merely swinging the movable reflecting mirror as one of the components of the lighting device unit in the horizontal directions can illuminate the fore scene with an insufficient amount of light in the turning direction of the vehicle. When the vehicle runs on a curved road with a small radius of curvature or turns at the intersection, it is necessary to greatly turn the movable reflecting mirror in the horizontal directions. When it is greatly turned, a light distribution pattern is greatly deformed, however. In this condition, it is difficult for the beam to illuminate the fore scene in a light distribution pattern which reflects current, incessantly varying vehicle running conditions.
Further, the technique of merely displacing the light distribution pattern in the horizontal directions is insufficient in securing the beam illumination in a light distribution pattern which reflects current, incessantly varying vehicle running conditions. When the vehicle speed is relatively low, an observation point of a driver is present at a relatively short distant region on the road surface in front of a vehicle. As the vehicle speed increases, the driver's observation point gradually moves to a distant point. For this reason, it is desirable to vertically move the illumination point of the light distribution pattern with the movement of the observation point. The technique of merely displacing the light distribution pattern in the horizontal directions, however, fails to satisfy such a desirable requirement.